TRANSITION TO SPIRAL-DEFECT CHAOS IN LOW PRANDTL NUMBER CONVECTION

We report a distinct transition at ε0.55 from a state with dislocation defects to spiral-defect chaos in a Rayleigh-Bénard system of aspect ratio Γ=40. The transition occurred over a narrow range in ε and was seen in angle-time representations of azimuthal power spectra, in the spatially averaged roll curvature, in the skewness of the structure function, and in the roll-nucleation frequency of sidewall foci. Comparison with work by others shows that the onset of spiral-defect chaos moves to smaller ε as Γ increases. © 1995 The American Physical Society.